Project description:X chromosome dosage compensation in Drosophila requires chromosome-wide coordination of gene activation. The male-specific-lethal dosage compensation complex (DCC) identifies X chromosomal High Affinity Sites (HAS) from which it reaches out to boost transcription. A recently discovered sub-class of HAS, PionX sites, represent first contacts on the X. We explored the chromosomal interactions of representative PionX sites by high-resolution 4C methodology and determined the overall chromosome conformation by Hi-C in sex-sorted embryos. X chromosomes from male and female cells display similar nuclear architecture, concordant with clustered, constitutively active genes. PionX sites, like HAS, are evenly distributed in the active compartment and engage in short- and long-range interactions beyond compartment boundaries. De novo induction of DCC in female cells allowed monitoring the reach of activation surrounding PionX sites. Remarkably, DCC not only activates genes in linear proximity, but also at megabase distance if close in space, suggesting that dosage compensation profits from chromosome folding.
Project description:Transcription regulators select their genomic binding sites from a large pool of similar, non‑functional sequences. Although general principles that allow such discrimination are known, the complexity of DNA elements often precludes a prediction of functional sites. The process of dosage compensation in Drosophila allows exploring the rules underlying binding site selectivity. The male-specific-lethal (MSL) Dosage Compensation Complex selectively binds to some 300 X-chromosomal ‘High Affinity Sites’ (HAS) containing GA‑rich ‘MSL recognition elements’ (MREs), but disregards thousands of other MRE sequences in the genome. The DNA‑binding subunit MSL2 alone identifies a subset of MREs, but fails to recognize most MREs within HAS. The ‘Chromatin-linked adaptor for MSL proteins’ (CLAMP) also interacts with many MREs genome‑wide and promotes DCC binding to HAS. Using genome‑wide DNA‑immunoprecipitation we describe extensive cooperativity between both factors, depending on the nature of the binding sites. These are explained by physical interaction between MSL2 and CLAMP. In vivo, both factors cooperate to compete with nucleosome formation at HAS. The male‑specific MSL2 thus synergises with a ubiquitous GA‑repeat binding protein for refined X/autosome discrimination.
Project description:The essential process of dosage compensation, which corrects for the imbalance in X-linked gene expression between XX females and XY males, represents a key model for how genes are targeted for coordinated regulation. However, the mechanism by which dosage compensation complexes identify the X-chromosome during early development remained unknown because of the difficulty of sexing embryos prior to zygotic transcription. We used meiotic drive to sex Drosophila embryos prior to zygotic transcription and ChIP-seq to measure dynamics of dosage compensation factor targeting. The Drosophila Male-Specific Lethal dosage compensation complex (MSLc) requires the ubiquitous zinc-finger protein Chromatin-Linked Adaptor for MSL Proteins (CLAMP) to identify the X-chromosome. We observe a multi-stage process in which MSLc first identifies CLAMP binding sites throughout the genome followed by concentration at the strongest X-linked MSLc sites. We provide insight into the dynamic mechanism by which a large transcription complex identifies its binding sites during early development.
Project description:In Drosophila, two chromosome-wide compensatory systems have been characterized; the dosage compensation system acting on the male X-chromosome and the chromosome specific regulation of genes located on the heterochromatic 4th chromosome. Dosage compensation in Drosophila is accomplished by hypertranscription of the single male X-chromosome mediated by the MSL-complex. The mechanism for this compensation is suggested to be an MSL-complex mediated enhanced transcriptional elongation while the mechanism for the compensation mediated by Painting of fourth (POF) on the 4th chromosome has remained elusive. Here we show that POF binds to nascent RNA and this binding is associated with an increase in amount of chromosome 4 transcripts. Furthermore, genes located on the 4th chromosome are enriched in binding of the nucleoplasmic nucleporin component NUP98 and this enrichment correlates to increased POF binding. We also show that genes located in heterochromatic regions have a shorter transition time from site of transcription and to the nuclear envelope. Our current work broadens the understanding about how genes in heterochromatic regions can overcome the repressive influence of their hostile environment.
Project description:Drosophila X chromosomes are subject to dosage compensation in males and are known to have a specialized chromatin structure in the male soma. We are interested in how specific chromatin structure change contributes to X chromosome hyperactivity and dosage compensation. We have conducted a global analysis of localize two dosage compensation complex dependent histone marks H4AcK16 and H3PS10 and one dosage compensation complex independent histone mark H3diMeK4 in the genome, especially on X chromosome by ChIP-chip approach in both male and female adult flies. We also probed general genomewide chromatin structure by deep DNA sequencing of sheared ChIP input DNA from male and female adult flies.
Project description:In Drosophila, two chromosome-wide compensatory systems have been characterized; the dosage compensation system acting on the male X-chromosome and the chromosome specific regulation of genes located on the heterochromatic 4th chromosome. Dosage compensation in Drosophila is accomplished by hypertranscription of the single male X-chromosome mediated by the MSL-complex. The mechanism for this compensation is suggested to be an MSL-complex mediated enhanced transcriptional elongation while the mechanism for the compensation mediated by Painting of fourth (POF) on the 4th chromosome has remained elusive. Here we show that POF binds to nascent RNA and this binding is associated with an increase in amount of chromosome 4 transcripts. Furthermore, genes located on the 4th chromosome are enriched in binding of the nucleoplasmic nucleporin component NUP98 and this enrichment correlates to increased POF binding. We also show that genes located in heterochromatic regions have a shorter transition time from site of transcription and to the nuclear envelope. Our current work broadens the understanding about how genes in heterochromatic regions can overcome the repressive influence of their hostile environment. Pof mutant vs. wild type, 3 replicates
Project description:In Drosophila, two chromosome-wide compensatory systems have been characterized; the dosage compensation system acting on the male X-chromosome and the chromosome specific regulation of genes located on the heterochromatic 4th chromosome. Dosage compensation in Drosophila is accomplished by hypertranscription of the single male X-chromosome mediated by the MSL-complex. The mechanism for this compensation is suggested to be an MSL-complex mediated enhanced transcriptional elongation while the mechanism for the compensation mediated by Painting of fourth (POF) on the 4th chromosome has remained elusive. Here we show that POF binds to nascent RNA and this binding is associated with an increase in amount of chromosome 4 transcripts. Furthermore, genes located on the 4th chromosome are enriched in binding of the nucleoplasmic nucleporin component NUP98 and this enrichment correlates to increased POF binding. We also show that genes located in heterochromatic regions have a shorter transition time from site of transcription and to the nuclear envelope. Our current work broadens the understanding about how genes in heterochromatic regions can overcome the repressive influence of their hostile environment.
Project description:The dosage compensation complex (DCC) of Drosophila identifies its X chromosomal binding sites with exquisite selectivity. The principles that assure this vital targeting are known from the D. melanogaster model: DCC-intrinsic specificity of DNA binding, cooperativity with the CLAMP protein, and non-coding roX2 RNA transcribed from the X chromosome. We found that in D. virilis, a species separated from melanogaster by 40 million years of evolution, all principles are active, but contribute differently to X-specificity. In melanogaster, the DCC subunit MSL2 evolved intrinsic DNA-binding selectivity for rare PionX sites, which mark the X chromosome. In virilis, PionX sites are abundant and not X-enriched. Accordingly, MSL2 lacks specific recognition. Here, roX2 RNA plays a more instructive role, counteracting a non-productive interaction of CLAMP and modulating DCC binding selectivity. Remarkably, roX2 triggers a low-diffusion chromatin binding mode characteristic of DCC. Evidently, X-specific regulation is achieved by divergent evolution of similar components.